Substantial advances have been made in automating the job of counting blood cells in a serum sample. The most well-known instrument for performing blood counts is the so-called Coulter counter in which blood cells are passed in single file through an orifice and detected and counted by the manner in which they change the electric properties at the orifice. Up until the present time, however, there has been no automated equipment available for analyzing and evaluating the multiple cells, such as, normal cells, target cells, sickle cells, etc. which may be found in a flowing stream of a given blood sample. Thus, where multiple cell information of this type is desired, the standard commercial way of obtaining it is by preparing a microscope slide with the cells fixed on an image plane and having a human operator or pattern recognition machine count statistically significant numbers of the cells as the cells are observed one-at-a-time on the slide through a microscope.
Some attempts have been made in recent years to provide optical analysis of particles flowing in a flow stream. For instance, Kay, et al., Journal of Histochemistry and Cytochemistry, Volume 27, page 329 (1979) shows a Coulter type orifice for moving cells in single file with the cells magnified on a vidicon. Additionally, Kachel, et al., Journal of Histochemistry and Cytochemistry, Volume 27, page 335, shows a device for moving cells in single file through a microscopic area where they are photographed. While these workers have done some work in automating particle analysis in single file no successful work has been reported where automated particle analysis was accomplished in a flowing stream without the requirement of arranging the particles into a single file stream. See for instance Flow Cytometry and Sorting Melaned et al, John Wiley & Sons 1979, Chapter 1.